Eye glasses are manufactured by inserting glass lens into a glass frame. The glass lens is selected according to a user's eyesight and the glass frame is selected according to the user's taste. In manufacturing the eye glasses, a blank lens of a circular shape is grinded to be suitable for the glass frame and then the grinded surface of the lens is polished. For these, a tracer, a blocker and a lens edger etc. are used. The tracer is for reading the contour of the glass frame, and the lens edger is for grinding the blank lens to be suitable for the shape of the glass frame. For grinding the blank lens with the lens edger, the blank lens must be firmly fixed to the lens edger so as to prevent the sliding of the blank lens during the lens grinding process. Accordingly, a block, which works as a double-faced tape, is adhered to the blank lens for fixing the blank lens to the lens edger through the block. According to the process type of the lens edger, the block can be adhered to an optical center of the blank lens or can be adhered to a location corresponding to the center of the glass frame.
A lens blocking apparatus (a lens blocker) for adhering the block can be classified into a manual lens blocking apparatus, a semi-automatic lens blocking apparatus and an automatic lens blocking apparatus. In operating the manual lens blocking apparatus, an operator marks an optical center of a blank lens on the surface of the blank lens by using a lensmeter. Then, the operator arranges the optical center of the blank lens and the block, or arranges the location corresponding to the center of the glass frame and the block, while observing through a viewing window which is mounted on the lens blocking apparatus. Thereafter, a block holder on which the block is mounted is allowed to move downwardly to adhere the block to the lens surface. In operating the semi-automatic lens blocking apparatus, the operator marks an optical center of a blank lens on the surface of the blank lens by using a lensmeter. Then, the marked lens is located on a lens supporter of the lens blocking apparatus, and the lens supporter is manually moved to a position at which the blocking process is performed. In the semi-automatic lens blocking apparatus, the blocking process is performed only at the one position. On the other hand, the automatic lens blocking apparatus have a lensmeter and an image processing part therein. Thus, when a blank lens is placed on a lens supporter, the optical center of the lens is automatically searched and then blocking process is performed on the optical center of the blank lens or on the location of the blank lens corresponding to the center of the glass frame. In the manual lens blocking apparatus, all operations are manually performed while observing through the viewing window, and the precision of the blocking process depends on the operator's skill or mistake. In the semi-automatic lens blocking apparatus, the blocking operation is automatically performed, and the precision of the blocking process less depends on the operator's skill or mistake. However, since the optical center of the lens is manually moved for the blocking process, the operator's skill or mistake still affect the performance of the blocking process.